Programmatically create new variables using purrr? - r

Question

Intro
After recently taking Hadley Wickham's functional programming class I decided I'd try applying some of the lessons to my projects at work. Naturally, the first project I tried has proven to be more complicated than the examples worked demonstrated in the class. Does anyone have recommendations for a way to use the purrr package to make the task described below more efficient?
Project Background
I need to assign quintile groups to records in a spatial polygon dataframe. In addition to the record identifier there are several other variables and I need to calculate the quintile group for each.
Here's the crux of the problem: I have been asked to identify outliers in one particular variable and to omit those records from the entire analysis as long as it doesn't change the quintile composition of the first quintile group for any of the other variables.
Question
I have put together a dplyr pipeline (see the example below) that performs this checking process for a single variable, but how might I rewrite this process so that I can efficiently check each variable?
EDIT: While it is certainly possible to change the shape of the data from wide to long as an intermediary step, in the end it needs to return to its wide format so that it matches up with the #polygons slot of the spatial polygons dataframe.
Reproducible Example
You can find the complete script here: https://gist.github.com/tiernanmartin/6cd3e2946a77b7c9daecb51aa11e0c94
Libraries and Settings
library(grDevices) # boxplot.stats()
library(operator.tools) # %!in% logical operator
library(tmap) # 'metro' data set
library(magrittr) # piping
library(dplyr) # exploratory data analysis verbs
library(purrr) # recursive mapping of functions
library(tibble) # improved version of a data.frame
library(ggplot2) # dot plot
library(ggrepel) # avoid label overlap
options(scipen=999)
set.seed(888)
Load the example data and take a small sample of it
data("metro")
m_spdf <- metro
# Take a sample
m <-
metro#data %>%
as_tibble %>%
select(-name_long,-iso_a3) %>%
sample_n(50)
> m
# A tibble: 50 x 10
name pop1950 pop1960 pop1970 pop1980 pop1990
<chr> <dbl> <dbl> <dbl> <dbl> <dbl>
1 Sydney 1689935 2134673 2892477 3252111 3631940
2 Havana 1141959 1435511 1779491 1913377 2108381
3 Campinas 151977 293174 540430 1108903 1693359
4 Kano 123073 229203 541992 1349646 2095384
5 Omsk 444326 608363 829860 1032150 1143813
6 Ouagadougou 33035 59126 115374 265200 537441
7 Marseille 755805 928768 1182048 1372495 1418279
8 Taiyuan 196510 349535 621625 1105695 1636599
9 La Paz 319247 437687 600016 809218 1061850
10 Baltimore 1167656 1422067 1554538 1748983 1848834
# ... with 40 more rows, and 4 more variables:
# pop2000 <dbl>, pop2010 <dbl>, pop2020 <dbl>,
# pop2030 <dbl>
Calculate quintile groups with and without outlier records
# Calculate the quintile groups for one variable (e.g., `pop1990`)
m_all <-
m %>%
mutate(qnt_1990_all = dplyr::ntile(pop1990,5))
# Find the outliers for a different variable (e.g., 'pop1950')
# and subset the df to exlcude these outlier records
m_out <- boxplot.stats(m$pop1950) %>% .[["out"]]
m_trim <-
m %>%
filter(pop1950 %!in% m_out) %>%
mutate(qnt_1990_trim = dplyr::ntile(pop1990,5))
# Assess whether the outlier trimming impacted the first quintile group
m_comp <-
m_trim %>%
select(name,dplyr::contains("qnt")) %>%
left_join(m_all,.,"name") %>%
select(name,dplyr::contains("qnt"),everything()) %>%
mutate(qnt_1990_chng_lgl = !is.na(qnt_1990_trim) & qnt_1990_trim != qnt_1990_all,
qnt_1990_chng_dir = if_else(qnt_1990_chng_lgl,
paste0(qnt_1990_all," to ",qnt_1990_trim),
"No change"))
With a little help from ggplot2, I can see that in this example six outliers were identified and that their omission did not affect the first quintile group for pop1990.
Importantly, this information is tracked in two new variables: qnt_1990_chng_lgl and qnt_1990_chng_dir.
> m_comp %>% select(name,qnt_1990_chng_lgl,qnt_1990_chng_dir,everything())
# A tibble: 50 x 14
name qnt_1990_chng_lgl qnt_1990_chng_dir qnt_1990_all qnt_1990_trim
<chr> <lgl> <chr> <dbl> <dbl>
1 Sydney FALSE No change 5 NA
2 Havana TRUE 4 to 5 4 5
3 Campinas TRUE 3 to 4 3 4
4 Kano FALSE No change 4 4
5 Omsk FALSE No change 3 3
6 Ouagadougou FALSE No change 1 1
7 Marseille FALSE No change 3 3
8 Taiyuan TRUE 3 to 4 3 4
9 La Paz FALSE No change 2 2
10 Baltimore FALSE No change 4 4
# ... with 40 more rows, and 9 more variables: pop1950 <dbl>, pop1960 <dbl>,
# pop1970 <dbl>, pop1980 <dbl>, pop1990 <dbl>, pop2000 <dbl>, pop2010 <dbl>,
# pop2020 <dbl>, pop2030 <dbl>
I now need to find a way to repeat this process for every variable in the dataframe (i.e., pop1960 - pop2030). Ideally, two new variables would be created for each existing pop* variable and their names would be preceded by qnt_ and followed by either _chng_dir or _chng_lgl.
Is purrr the right tool to use for this? dplyr::mutate_? data.table?

Answer 1

It turns out this problem is solvable using tidyr::gather + dplyr::group_by + tidyr::spread functions. While #shayaa and #Gregor didn't provide the solution I was looking for, their advice helped me course-correct away from the functional programming methods I was researching.
I ended up using #shayaa's gather and group_by combination, followed by mutate to create the variable names (qnt_*_chng_lgl and qnt_*_chng_dir) and then using spread to make it wide again. An anonymous function passed to summarize_all removed all the extra NA's that the wide-long-wide transformations created.
m_comp <-
m %>%
mutate(qnt = dplyr::ntile(pop1950,5)) %>%
filter(pop1950 %!in% m_out) %>%
gather(year,pop,-name,-qnt) %>%
group_by(year) %>%
mutate(qntTrim = dplyr::ntile(pop,5),
qnt_chng_lgl = !is.na(qnt) & qnt != qntTrim,
qnt_chng_dir = ifelse(qnt_chng_lgl,
paste0(qnt," to ",qntTrim),
"No change"),
year_lgl = paste0("qnt_chng_",year,"_lgl"),
year_dir = paste0("qnt_chng_",year,"_dir")) %>%
spread(year_lgl,qnt_chng_lgl) %>%
spread(year_dir,qnt_chng_dir) %>%
spread(year,pop) %>%
select(-qnt,-qntTrim) %>%
group_by(name) %>%
summarize_all(function(.){subset(.,!is.na(.)) %>% first})

Answer 2

Nothing wrong with your analysis it seems to me,
After this part
m <- metro#data %>%
as_tibble %>%
select(-name_long,-iso_a3) %>%
sample_n(50)
Just melt your data and continue your analysis but with group_by(year)
library(reshape2)
library(stringr)
mm <- melt(m)
mm[,2] <- as.factor(str_sub(mm[,2],-4))
names(mm)[2:3] <- c("year", "population")
e.g.,
mm %>% group_by(year) %>%
+ mutate(qnt_all = dplyr::ntile(population,5))